Kinetic Analysis of Oleic Acid Esterification Using Lipase as Catalyst in a Microaqueous Environment

Abstract

This paper reports the lipase-catalyzed esterification of oleic acid (with ethanol) in a batch reactor at temperatures between 298 and 338 K using a wide range of the reactant ratio, β (0 < β < 2). All kinetic runs were performed under conditions of negligible transport limitations. The sigmoidal behavior evidenced from the initial rate-substrate concentration curve suggests the allosteric nature of the acrylic-supported Aspergillus lipase, and hence, the data were described by a non-Michaelis Menten kinetic model. The associated oleic acid binding coefficient and ethanol inhibition constant were obtained as 2.382 and 1.643 mmol L -1 , respectively. The allosteric effect was attributed to conformational change in the enzyme site occasioned by the presence of trace amounts of water formed within the first few minutes of the reaction. Indeed, the transient water concentration profile at different β values revealed an initial overshoot in water concentration before the relaxation to final equilibrium value after about 6 h. The appearance of the initial overshoot increased with decreasing β. The water concentration history is symptomatic of two first-order interacting processes fed by a self-propagating input consistent with the two-enzyme state concerted symmetry proposition for nonlinear feedback autoregulatory behavior. The rate-temperature envelope showed a maximum at about 318 K, suggesting protein denaturation above this temperature. Even so, a fit of the rate data obtained between 298 to 318 K gave an activation energy of 22.4 kJ mol -1 , typical of many enzymatic reactions. FTIR spectra of the catalysts displayed peaks at 1723.23 and 1666.12 cm -1 assigned to COOand NH 2 + groups, respectively, for both fresh and used specimens. BET measurements, however, revealed a significant drop in surface area between fresh (165 m 2 g -1 ) and used (5-20 m 2 g -1 ) catalysts. This was attributed to pore blockage of the immobilized enzyme by the relatively large oleic-acyl-lipase complex left after the reaction.

Valorization of Agro-Industrial Residues: Bioprocessing of Animal Fats to Reduce Their Acidity

“…Even for Novozym 435, the assumption of a homogeneous medium is valid, as the combination of very small particles with strong mixing ensures that the external and internal diffusional resistances are minimal and the reactional system is under chemical control (catalyst efficiency equal to one). As considered above, the free fatty acids present in the lard and tallow mixture are considered to be well-represented by oleic acid (C18:1), supported by the analysis of the fatty acids profile of fat sample performed in this study, and others available in literature [42][43][44]. Thus, as a proxy, it was assumed that the FFA concentration is equivalent to the same concentration of oleic acid [42][43][44][45], calculated as follows.…”

Effect of light irradiation on esterification of oleic acid with ethanol catalyzed by immobilized Pseudomonas cepacia lipase

“…This similar mechanism was also used by Chulalaksananukul et al and Martinelle and Hult to explain the kinetic study with competitive inhibition by the acyl acceptor or donor. In addition, Mahmud et al used an Aspergillus lipase catalyzed reaction to compare the Ping‐Pong Bi‐Bi mechanism with three different models proposed by Foresti et al using Candida Antarctica B , Paiva et al and Chulalaksananukul et al using Mucor meihei on oleic acid esterification. In the present study, the double reciprocal plot of the initial esterification rate at various ethanol (and oleic acid) concentrations generates a set of nearly parallel lines (Figure S2).…”

Basket Impeller Extractive Reactor Column for Biodiesel Production: An Experimental Study

“…Allosteric effect during lipasic esterification of oleic acid has been previously reported in our laboratory. 29 However, the observed concentration oscillations were not mirrored in the extract phase, probably because of the relatively high water and ethanol content in this aqueous phase, which rendered the transient changes less detectable.…”

“…This behavior is commonly found in many natural (biological, 25−27 physical, and chemical 28,29 ) systems and may be captured by the threeparameter sigmoidal expression:…”